This invention relates to a thin film magnetic head and in particular to a magnetic head using amorphous magnetic alloy thin films suitable for a high density recording.
A thin film magnetic head is constructed, in general, by superposing successively a lower magnetic film, a gap non-magnetic film, an interlayer insulating film, a conductor coil, an interlayer insulating film, an upper magnetic film and finally a non-magnetic protecting film on a non-magnetic substrate made of ceramic by applying thin film techniques. Recording in and reproduction from the recording medium are effected usually by means of a single thin film magnetic head.
The working principle of this thin film magnetic head consists in that when information is written in the recording medium, a signal current is made flow through the conductor coil, which generates a high magnetic field at the magnetic gap of the magnetic films exposed at the extremity of the thin film magnetic head and magnetizes selectively the recording medium moving in the neighborhood of the exposed part at the extremity. On the contrary, when the information stored in the recording medium is read out, the selectively magnetized recording medium is moved in the neighborhood of the magnetic gap, which produces variations in magnetic flux in the magnetic core composed of the two magnetic films, which generates a voltage across the conductor coil.
The recording density is made higher with increasing speed of writing and reading information in and from such recording medium. For this purpose it is required that the magnetic films have magnetic characteristics such as a low coercive force, a magnetic field of low anisotropy and, at the same time, a high saturated magnetic flux density, and to be made of a material having a low magnetostriction constant.
The magnetic hysteresis loop becomes narrower with decreasing coercive force and the magnetization is more rapid and easy with a magnetic field of decreasing anisotropy. Further the magnetic field produced by the magnetic head and contributing to the recording is stronger and more abrupt with increasing saturated magnetic flux density, by which information is recorded with a high resolution. In addition, variations in the magnetic characteristics such as the permeability, the coercive force, etc. are smaller with decreasing magnetostriction constant, corresponding to remaining stress due to the difference in the thermal expansion coefficient between the magnetic films and the substrate at the formation thereof or to external stress due to mechanical working, which stabilizes record reading-out and writing-in characteristics.
Heretofore, primarily a permalloy (80Ni-Fe) film deposited by plating, evaporation or sputtering, whose saturated magnetic flux density is about 1.0 Tesla (T), is used as magnetic core material for the thin film magnetic head. However, with this permalloy film, whose saturated magnetic flux density is about 1.0 T, there is a limit to increasing the recording density. Therefore, it is not possible to satisfactorily deal with requirements to increase the capacity and the recording density for a large scale electronic computer by using conventional magnetic core materials. Thus, it is desired to find a material having a saturated magnetic flux density higher than 1.3 T.
Furthermore, it is thought that the magnetic characteristics required for the core material for the thin film magnetic head are an excellent uniaxial anisotropy, an anisotropy field as low as 3 to 5 Oersted (Oe) to increase the permeability and a coercive force in the direction of the axis of hard magnetization smaller than 1 Oe. What is more important is that the magnetostriction constant is brought as closely as possible to zero in order that the magnetic head is hardly influenced by external stress. It is thought that the magnetostriction constant should preferably be between +0.5.times.10.sup.-6 and -2.0.times.10.sup.-6, taking into account the shape of the magnetic core or the relation to the stress in an Al.sub.2 O.sub.3 film deposited on the magnetic core by sputtering.
In order to fulfill these requirements, various sorts of developments using amorphous alloy films are carried out, because the amorphous alloy film has no magnetocrystalline anisotropy. Among them, amorphous alloy thin films of metal-metal system such as Co-Zr system or Co-Hf system, whose saturated magnetic flux density can be higher than 1.3 T, have been found. However, since they have a magnetostriction constant which is positive and as great as 2.times.10.sup.-6, there have been proposed tertiary amorphous films including Nb, Ta, W, etc., which are known as elements reducing magnetostriction constant, in addition to the binary systems described above. As representatives thereof, there are known magnetic heads using amorphous films of Co-Zr-Ta or those using amorphous films of Co-Hf-Ta, as disclosed in Japanese patent unexamined publications JP-A-60-21504 and JP-A-60-22722.
However, since these tertiary amorphous alloys of Co-Zr-Ta and Co-Hf-Ta systems contain a large amount of Zr, Ta, etc., which are easily oxidized, they have a weakness in the corrosion resistance thereof because of the fact that Zr, Ta, etc. are oxidized due to the humidity in the atmosphere. Therefore, the films loose their magnetic characteristics, which gives rise to a problem that they lack high reliability as a material used in a thin film magnetic head.
Furthermore, since the Co-Hf-Ta tertiary system has a very narrow composition area in which the saturated magnetic flux density is high and the magnetostriction constant is reduced to the proximity of zero, it has a problem that it is difficult to stably form magnetic films for a thin film magnetic head.